1. Field of the Invention
The present invention relates to an electric motor.
2. Description of Related Art
Conventional electric motors have annular stators. The stator has an annular stator core around which a coil is wound. The stator core is composed of a laminated steel plate. The laminated steel plate is an assembly obtained by laminating a number of silicon steel plates in an axial direction of the stator. In some cases, the stator core may be composed of a powder molding including a powder magnetic material and obtained by compression molding. Further, in some cases, the stator core may be composed of an assembly of a laminated steel plate and the powder molding described above (e.g., Japanese Unexamined Patent Publication No. 2002-369418).
When the stator core is composed of the laminated steel plate, however, the outer shape of the stator core is a round pillar shape. The coil projects from both ends of the stator core in the axial direction. As a result, an empty space occurs around the coil. On the other hand, in the stator core composed of the laminated steel plate, flexibility of the shape of the stator core is low in a lamination direction corresponding to the axial direction of the stator core. Therefore, the empty space that occurs around the coil cannot be solved. Consequently, a magnetic flux is not effectively utilized, so that the output torque of the electric motor is reduced. Conversely, an attempt to increase the output torque increases the electric motor in size.
When the stator core is composed of the above-mentioned powder molding, the flexibility of the shape is high, while the manufacturing cost is high.
In the foregoing document, powder moldings are each arranged at both ends of the laminated steel plate in an axial direction of the stator core. Since a coil is wound in a state where the coil projects in the axial direction of the stator core from the powder molding, an empty space described above occurs around the coil. As a result, the output torque is reduced.
An object of the present invention is to provide a low-cost electric motor that can be inhibited from increasing in size and can increase output torque.